1. Field of the Invention
The present invention relates to a novel compound and organic light emitting diode using the same, particularly to 6H-indolo[2,3-b]quinoxaline derivative and organic light emitting diode using the same.
2. Description of the Prior Art
OLED works on the principal that electrons and holes diffuse through an electron transport layer (ETL) and hole transport layer (HTL), respectively, to enter an light-emitting layer, and recombine in the emitting region to form a particle generally referred as exciton. In order for the exciton to relax to the ground state, the energy is given off in the form of photo radiation. The radiation color can be tuned by applying different emitting materials. OLED has been highly-regarded due to a lot of advantages, such as self illumination, wider visual angle (>170°), shorter response time (˜μs), higher contrast, higher efficiency, lower power consumption, higher brightness, lower operative voltage (3-10V), thinner size (<2 mm), flexibility and so on.
The exciton generated from recombining holes and electrons may have triplet state or singlet state for its spin state. The singlet exciton relaxation would radiate fluorescence, and the triplet exciton relaxation would radiate phosphorescence. The phosphorescence has triple lighting efficiency in comparison to fluorescence, and metal complexes may be used in the emitting layer so as to form strong spin-orbital coupling, whereby combined singlet and triplet excited states causes elevated IQE (internal quantum efficiency), 100%, within the device. Therefore, phosphorescent metal complexes have been used as phosphorescent dopants in light-emitting layer. In addition, by using a doping method in the emitting layer, self-quenching of the emitting materials can be reduced greatly to enhance the efficiency of the device. Therefore, the search for proper phosphorescent host materials becomes noteworthy since host materials must be capable of capturing carriers and have good energy transfer properties, high glass transition temperature, high thermal stability and appropriate energy gap of the singlet and triplet excited states. However, it would be difficult to search for host materials that fully meet the criteria and there is still some room for host materials development in OLED.
To sum up, to develop novel host materials is now a current goal.